In a method for improving the heat conductivity of heat transport medium, it is known to mix liquid with metal system nanometric particles whose diameter is on a nanometer order. See J. Heat Transfer 121, pp. 280-289 (1999). For a liquid including metal system nanometric particles, metal oxides which are added to a base liquid include, for example, Al2O3, CuO, TiO2, Fe2O3, whose diameter is less than or equal to 100 nm. Further, an interfacial active agent is used; for example dodecyl sodium sulfate, sodium polyacrylate, to keep dispersal stable.
However, metal system nanometric particles of 1-10 wt % relative to the heat transport medium need to be added to improve the heat conductivity of liquid, and adding a large amount of metal system nanometric particles increases the kinetic viscosity of the liquid severely. The increase of the kinetic viscosity of the liquid increases the energy consumption of the pump to circulate the fluid, and an increase in friction resistance occurs. Therefore, this increase causes some problems, for example, heat exchange efficiency and the amount of heat release decrease, thus preventing the improvement of heat conductivity.
Another liquid is known. It comprises solubilized carbon nanotubes in a base liquid, instead of metal system nanometric particles. In detail, in this technology, carbon nanotubes are solubilized in a base liquid by acid treatment on the surface of carbon nanotubes. See Japanese Patent Application Publications JP2003-95624, JP2003-300715, JP2003-300716, JP2004-168570 and JP2004-216516.
However, under this technology, adding a small amount of carbon nanotubes into the base liquid causes a decrease in pH to 5-6 because of the acid treatment on the surface of carbon nanotubes. Therefore, the liquid is a corrosive and there is a problem that it is necessary to provide or maintain acid-resistance for the system with the heat transport medium.
Another liquid is also known. Solubilization technology of carbon nanotubes by a basic polymer comprising an amino base or a fluorine polymer as dispersant is shown. See Japanese Patent Application Publication JP2004-261713.
However, this heat transport medium also comprises general anti-corrosion material to prevent corrosion of metal pipework parts making up the flow passage. Therefore, there is a possibility that the dispersant and anti-corrosion material react chemically and cause problems, for example deposition, decomposition, transmutation and formation of a supernatant. Further, these polymers have poor heat resistance in view of the application for heat transport medium because they can decompose or burn under 200° C.